陶瓷/纤维/树脂超混杂复合材料的力学性能

以泡沫SiC陶瓷为基本骨架,以改性酚醛树脂为基体,加入短切高硅氧玻璃纤维制备出陶瓷/纤维/树脂超混杂复合材料(SHCM),研究了泡沫陶瓷骨架和高硅氧纤维对材料力学性能的影响.结果表明,泡沫陶瓷骨架有利于材料的刚度和尺寸稳定性提高.加入泡沫陶瓷骨架后,纤维/树脂/陶瓷超混杂复合材料的压缩强度和压缩模量增大,随着泡沫陶瓷骨架含量的提高,弯曲模量大幅度提高而弯曲强度略有下降;随着高硅氧纤维含量的提高,材料的弯曲强度及弯曲模量均明显提高.     

高硅氧/酚醛复合材料热-力-化学多物理场耦合计算

基于高硅氧/酚醛复合材料体积烧蚀条件下的三维多物理场耦合控制方程,通过有限元方法预报了高硅氧/酚醛复合材料在酚醛树脂热解反应过程中的温度场、位移场、孔隙压力以及树脂残留率等热力学响应。计算结果表明：数值计算模型预报的温度场和位移场与高硅氧/酚醛复合材料高温变形实验的测量值吻合。材料热解过程中固体材料孔隙压力的峰值点出现在材料热解反应刚开始发生的区域,而弹性应力的峰值点出现在靠近材料热解层的原始材料层。     

ZrB2和POSS对碳布/酚醛复合材料烧蚀性能的影响

以ZrB2为改性剂,采用热压工艺制备了碳布/酚醛复合材料,通过氧/乙炔烧蚀实验对复合材料的烧蚀性能进行了研究,利用扫描电镜和能量色散谱仪对复合材料烧蚀形貌和成分进行了分析。结果表明:经氧/乙炔焰烧蚀后,在复合材料表面形成了一层陶瓷层,其质量烧蚀率为0.04585g/s,线烧蚀率为-0.013mm/s,经二次烧蚀后,复合材料的质量烧蚀率为0.0096g/s。当ZrB2和POSS配合使用改性碳布/酚醛复合材料时,碳布/酚醛复合材料的质量烧蚀率可达0.025g/s,二次质量烧蚀率可达0.0089g/s。     

玻璃微珠和ZrB2改性石英酚醛复合材料的耐烧蚀性能

在石英/酚醛防热复合材料中引入玻璃微珠和ZrB_2颗粒,旨在提高其耐冲刷、烧蚀性能。采用氧乙炔烧蚀试验测试所得石英/酚醛复合材料的耐烧蚀性能,对比分析了玻璃微珠和ZrB_2颗粒对低密度和全密度石英/酚醛材料烧蚀机理和烧蚀性能的影响。结果表明,在低密度石英酚醛复合材料中掺入适量的ZrB_2颗粒能使复合材料在烧蚀表面形成熔覆层,该熔覆层能有效保护碳化层及基体材料,降低线烧蚀率和质量烧蚀率。而表面熔覆层的形成与ZrO_2在硅系熔融物中产生的"钉锚效应"相关,同时也与B_2O_3降低硅系熔融物的表面能有关。在全密度石英酚醛复合材料中引入ZrB_2颗粒,可使其在烧蚀过程中形成多孔的ZrO_2层,有效地将碳化层和烧蚀环境隔离。然而,ZrO_2层没有熔融铺展,与碳化层结合力较弱,在烧蚀过程中容易剥落。     

CBF/S-157酚醛树脂复合材料的研究

对连续玄武岩纤维(CBF)增强S-157酚醛树脂复合材料进行了研究.考察了树脂含量、纤维单丝直径、纤维股数对CBF/S-157复合材料弯曲性能和烧蚀性能的影响,并借助扫描电镜对其烧蚀表面形貌进行了观察,同时将CBF/S-157复合材料与高硅氧玻璃纤维(简称HSGF)/S-157酚醛树脂复合材料的弯曲性能和烧蚀性能进行了对比.结果表明:树脂含量在30%时,CBF/S-157复合材料弯曲性能和烧蚀性能最佳;CBF/S-157复合材料和HSGF/S-157复合材料的烧蚀性能相近,但前者的弯曲性能明显好于后者.     

氧化石墨烯和石墨相氮化碳增强炭/酚醛复合材料界面热烧蚀性能对比

为了提高炭/酚醛复合材料的烧蚀性能,分别采用两种炭纳米填料对纤维增强体界面进行改性。以氧化石墨烯(GO)和酸化石墨相氮化碳(ag-C_3N_4)改性低负载(0.05 wt%～0.2 wt%)的炭/酚醛复合材料。用氧乙炔火焰、SEM、XRD、Raman研究烧蚀面形貌与纤维石墨化度。结果表明:随着GO和ag-C_3N_4含量由0升至0.2 wt%,GO/CF-PR和ag-C_3N_4/CF-PR复合材料的耐烧蚀性能均呈现先增加后降低的趋势。其中以0.1 wt%添加量为最佳,0.1ag-C_3N_4/CF-PR和0.1GO/CF-PR复合材料比起纯的CF-PR的质量烧蚀率分别降低44.42%和28.96%,归因于ag-C_3N_4和GO可显著提高基体的炭残率和烧蚀区纤维表面的石墨化度。     

含PyC-TaC-PyC复合界面C/C材料的氧乙炔焰烧蚀行为

用化学气相渗透方法，在准三维针刺炭毡中预沉积热解炭(PyC)和TaC涂层，再利用热解炭和树脂炭对该预制体进行后续致密化，制得含PyC-TaC-PyC复合界面的C/C复合材料(TaC-C/C)，并对其进行氧乙炔焰烧蚀。与C/C相比，3 vol%TaC-C/C材料耐烧蚀性能无明显提高，且无法承受长时间的氧炔焰烧蚀；而14 vol%TaC-C/C材料表现出较好的长时间耐烧蚀性能。氧炔焰烧蚀后，复合材料表面由C、TaC、(Ta，O)及Ta₂O₅相组成。3 vol%TaC-C/C材料表面主要形成细小弥散的烧蚀斑点(5～20s)和烧蚀凹坑(120s)；而14 vol%TaC-C/C材料表面则主要形成烧蚀斑点(5s)、较完整的氧化钽层(20s)以及烧蚀凹坑(120s)。14 vol%TaC-C/C材料在烧蚀20s后，复合材料可分为表面氧化物区、过渡区和基体区；复合材料表面完整连续的氧化钽层能有效保护复合材料。     

硅改性酚醛/碳纤维复合材料的制备及烧蚀性能

针对酚醛树脂(RF)耐热性不足、抗烧蚀性能差,且SiO₂粒子与酚醛树脂相容性的问题,采用共凝胶法制备纳米级的SiO₂/RF杂化气凝胶,通过构建凝胶网络互穿结构,增加两相相容性,探究SiO₂/RF杂化气凝胶的微观结构、化学结构和热物理性能。制备得到硅改性酚醛/碳纤维复合材料,并对改性前后复合材料的烧蚀性能进行比较。结果表明,不同硅含量的杂化气凝胶具有凝胶骨架和孔隙双连续的结构特性,密度分别在0.145～0.160 g/cm³之间。随着硅含量提高,杂化气凝胶残留率增加,Si—O键吸收振动峰更明显,但XRD无衍射峰。综合考虑孔径分布及热物理性能,选取性能最优的杂化气凝胶制备硅改性酚醛/碳纤维复合材料,改性后复合材料的质量烧蚀率为0.046 g/s,线烧蚀率为0.074 mm/s。与未改性的复合材料相比,质量烧蚀率降低了20.7%,线烧蚀率降低了21.3%,改性后材料的抗氧化性和烧蚀后的残留率得到明显提升。     

碳纤维丝束结构对碳纤维/酚醛复合材料烧蚀性能的影响EI北大核心CSCD

以酚醛树脂为基体,以平纹碳布和短切碳纤维两种结构形式的碳纤维为增强剂,制备碳纤维增强的碳/酚醛复合材料。采用氧/乙炔烧蚀实验对复合材料的耐烧蚀性能进行了对比性研究,采用电子拉力试验机对复合材料的弯曲性能进行表征,采用扫描电镜对复合材料烧蚀形面进行观察,并通过固体火箭发动机对复合材料的烧蚀性能进行考核验证。研究结果表明:以这两种结构形式的碳纤维为增强剂制备的碳/酚醛复合材料,其氧乙炔质量烧蚀率的大小与碳纤维丝束的大小具有正相关的特性,碳纤维丝束越小碳纤维质量烧蚀率越低,当碳纤维增强剂处于单丝状态时,复合材料的氧乙炔质量烧蚀率达到最低为0.046 g/s,并且碳纤维的型号规格对复合材料氧乙炔质量烧蚀率的影响变小。固体火箭发动机实验表明,单丝状态下的碳纤维/酚醛复合材料的抗烧蚀冲刷性能明显优于束状碳纤维/酚醛复合材料。     

酚醛改性苯并噁嗪树脂及其复合材料性能

从固化反应动力学、热分解动力学与耐烧蚀性能等方面研究了不同配比酚醛/苯并噁嗪共混树脂,并通过浸渍高硅氧玻璃布制备了相应的树脂复合材料。对其高常温力学、热学与耐烧蚀性能进行了研究。结果表明：共混树脂复合材料常温拉伸强度（214 MPa）、弯曲强度(332 MPa）、压缩强度(217 MPa）与高温层间剪切强度（21.6 MPa）等力学性能均高于酚醛树脂复合材料,热学与烧蚀性能符合耐烧蚀复合材料要求,可以作为一种性能优良的耐烧蚀复合材料。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.